Fogden, Andrew

Gujjari, Chamundi

Batchelor, Warren

Abstract [en]

To investigate the relationship between ink film splitting noise and ink tack, two tack-measuring devices were monitored by a microphone. The first of these was the Deltack(R) (Prufbau), to study tack build on paper, and the second was the Hydroscope(R) (Testprint), measuring ink tack change with fountain solution level. Three medium weight coated (MWC) papers and two heat-set inks of differing tack and emulsion capacity were analysed. It was concluded that acoustic average power is a consequence of cavitation and flow mechanisms, and not necessarily linked linearly to tack. The Hydroscope measurements usually gave decreasing tack, average power and average frequency with increasing fountain solution concentration; however fountain solution droplets can also act as an extra sound source. A relation between average frequency and droplet size was postulated. The results demonstrate the sensitivity of the acoustic method and support its implementation for further studies in the field.

Voltaire, Joakim

Abstract [en]

This thesis claims a relationship between the film splitting sound emission from the printing press nip and the dynamic interaction occurring there between ink, fountain solution and substrate in offset lithography. The film splitting sound derives from the cavitation formed by the pressure drop in the second half of the print nip flow passage. As the ink film is strained, the cavities expand and eventually implode into breaking filaments at the nip exit, while emitting a partly audible, broadband, high frequency, noisy sound. A free-field microphone, A/D-converter and laptop computer were used to record pressure signals in the frequency range of 10 Hz to 50 kHz emitted by a variety of printing instruments and presses for a range of offset ink and paper types. After signal acquisition and filtering two signal averages of power and frequency were estimated.

This average power increased with increasing loads of sheet-fed offset ink on an ink distributor, in accordance with a mass-conservation model developed. The behaviour of average frequency and power over different ink load ranges indicated transitions between different flow regimes. A glossy fine-coated paper gave higher average power than a corresponding matte paper during printing with such inks on a laboratory device, possibly due to an air sealing effect. The sound from tack measurements with the Deltack instrument during setting of heat-set offset inks printed on MWC papers showed a relation between the measured tack rise and average power, reflecting changes in splitting mechanism during the course of setting. With the Hydroscope instrument the interaction between these heat-set inks and fountain solution was studied, with the measured tack and sound emission displaying a clear, but non-linear, correlation. A heat-set offset pilot trial showed that the acoustic response from the printing nip sensitively and systematically detected changes in (LWC) paper type, optical density, ink-fount balance, and press stability. Pilot trials of cold-set offset inks on newsprint by sheet-fed presses indicated a strong correlation between evolution in average power, optical density and fountain solution consumption during the first thousand sheets normally needed for stabilisation.

Acoustic measurements of ink film splitting have, aside from the laboratory studies performed by one Japanese group, previously received little attention, with the current study showing that a great deal of information useful to the printer can be accessed from this sound emission. Although the detailed mechanisms for ink film splitting have to be further studied and supported by mathematical simulation, the sensitivity of the acoustic method recommends its implementation for monitoring and control of offset printing.